1. Field
One or more embodiments of the disclosure relate to a position adjustment apparatus of an imaging unit, the imaging unit, and an image reading apparatus including the imaging unit, and more particularly, to an image sensor that reads image information recorded on a document, a position adjustment apparatus of an imaging unit that adjusts a position of a focusing optics, and an image reading apparatus including the imaging unit.
2. Description of the Related Art
An image reading apparatus, such as a copier, a fax machine, and a scanner, irradiates light to a document, receives light reflected from the document by using an image sensor, reads image information, and converts the light into an electrical signal.
The image reading apparatus may include a light source that generates light, the image sensor that receives the light reflected from the document and converts the light into the electrical signal, and a focusing lens that is disposed on a light path from the light source and the image sensor and focuses a document image onto the image sensor.
A size of the image sensor is generally smaller than that of the document, and thus the focusing lens is generally a reduction optical system. For the image reading apparatus that uses the reduction optical system, it is very difficult to assemble the image sensor positioned in a rear end of the focusing lens at a position at which optimal focusing performance is implemented. This is because the sensitivity of a position change increases at a reciprocal number (i.e., inversely) of a reduction magnification due to characteristics of the reduction optical system.
For example, FIG. 1 is a perspective view of a conventional adjustment structure of an imaging unit of an image reading apparatus, and FIGS. 2A through 2C are conceptual diagrams of an image sensor 18 that is adjusted in upper and lower directions in the imaging unit of the conventional image reading apparatus of FIG. 1. Referring to FIGS. 1 through 2C, in the conventional adjustment structure, a focusing lens 12 is fixed to a fixing plate 11 by using a lens holder 13, and a sensor module substrate 14, on which the image sensor 18 is mounted, is installed and adjusted with respect to the fixing plate 11. If the sensor module substrate 14 adjusts an image skew and a Y-position through movement and rotation in upper and lower directions with respect to the fixing plate 11, the sensor module substrate 14 is fixed to the fixing plate 11 by using a fastening member such as a bracket 15 and a screw 16. In this case, reduced images of a rear end of the focusing lens 12 and the image sensor 18 are aligned, and thus adjustment sensitivity greatly increases. When the screw 16 is fixed after the adjustment, subtle movement and rotation of the bracket 15 that are caused by a rotation of the screw 16 lead to a very high skew error and Y-position error.
In more detail, when the focusing lens 12 and the image sensor 18 are aligned at a reference position, as shown in FIG. 2A, if a scan image read by the image sensor 18 is biased in a direction 21, as shown in FIG. 2B, the Y-position of the image sensor 18 is adjusted to a +Y-position so that the scan image read by the image sensor 18 may be positioned on a regular position. Likewise, when the scan image read by the image sensor 18 is biased in another direction 23, as shown in FIG. 2C, the Y-position of the image sensor 18 is adjusted to a −Y-position so that the scan image read by the image sensor 18 may be located on the regular position. A reflective mirror 19 guides a light path from a document image to the focusing lens 12 and the image sensor 18. When optics of the focusing lens 12 is a 0.1 reduction optical system, the document image having a width of 1 mm is focused as a 0.1 mm image in the rear end of the focusing lens 12. This means that a focusing accuracy is changed to 1 mm (that is 10 is obtained based on the inverse of 0.1 which corresponds to a reciprocal number of a reduction rate with respect to a position change of 0.1 mm of the image sensor 18). Deviations 20, 22 of the Y-position of the image sensor 18 cause deviations 21, 23 that are magnified by 10 times in a document. That is, according to the related art, the position of the image sensor 18 is adjusted in the rear end of the focusing lens 12, which results in an increase in the adjustment sensitivity as the reciprocal number (inverse) of the reduction rate of the reduction optical system.